Previously, with a view to preventing in advance the occurrence of an encountered collision accident or a rear-end accident between vehicles, a study of an inter-vehicle Communication system has been made, which transfers position information of each vehicle and vehicle operation information such as accelerator operation and brake operation between vehicles within a range of a predetermined distance, with each other through communication (RC-013 standards in Japan, CAM (Cooperative Awareness Message) and DENM (Decentralized Environmental Notification Message) standards in Europe, and BSM (Basic Safety Message) standards in USA, etc.). In such an inter-vehicle communication system, it is considered not only to perform communication by short-distance radio between vehicles approaching each other, but also to perform communication even between vehicles which are located apart from each other through an existing and/or new wireless communication network.
In such a wireless communication network, communication is usually performed by switching a communication state between a wireless base station and a terminal device which constitutes the wireless communication network to a standby state communicating only predetermined specified basic information or to a connecting state capable of communicating arbitrary information. For example, in the mobile communication (e.g., 3G/LTE, etc.) using a cellular wireless communication network which is an existing wireless communication network, it is known to take 100 milliseconds to a few seconds to switch from the standby state to the connecting state.
For this reason, in the case where inter-vehicle communication for the purpose of preventing in advance the occurrence of encountered collision accidents or rear-end accidents between vehicles as described above is performed through a wireless communication network, it is necessary to constantly hold the terminal device (i.e., vehicle-mounted communication device) and the wireless base station in the connecting state to instantly transfer the information in the case of the occurrence of an emergency state.
However, if each vehicle performs communication through the wireless communication network while constantly holding the connecting state to exchange operation information, there is a possibility that communication resources such as the wireless band and the communication capacity in the wireless communication network become tight and it is not possible to exchange necessary information, when needed, without delay.